上面的几个解决方案涉及到一些不必要的nsstring使用。这个UIColor类扩展更简单更快:

+ colorWithHex:(UInt32)hex alpha:(CGFloat)alpha
{
    return [UIColor colorWithRed:((hex & 0xFF0000) >> 16)/255.0
                           green:((hex & 0x00FF00) >> 8)/255.0
                            blue:( hex & 0x0000FF)/255.0
                           alpha:alpha];
}

简单来说:

return [UIColor colorWithHex:0x006400 alpha:1.0]; // HTML darkgreen

extension UIColor 
{
    class func fromHexaString(hex:String) -> UIColor
    {
        let scanner           = Scanner(string: hex)
        scanner.scanLocation  = 0
        var rgbValue: UInt64  = 0
        scanner.scanHexInt64(&rgbValue)

        return UIColor(
            red: CGFloat((rgbValue & 0xFF0000) >> 16) / 255.0,
            green: CGFloat((rgbValue & 0x00FF00) >> 8) / 255.0,
            blue: CGFloat(rgbValue & 0x0000FF) / 255.0,
            alpha: CGFloat(1.0)
        )
    }
}

//you can call like this.

UIColor.fromHexaString(hex:3276b1)

extension UIColor {
    convenience init(hexaString: String, alpha: CGFloat = 1) {
        let chars = Array(hexaString.dropFirst())
        self.init(red:   .init(strtoul(String(chars[0...1]),nil,16))/255,
                  green: .init(strtoul(String(chars[2...3]),nil,16))/255,
                  blue:  .init(strtoul(String(chars[4...5]),nil,16))/255,
                  alpha: alpha)}
}

用法:

let redColor       = UIColor(hexaString: "#FF0000")              // r 1,0 g 0,0 b 0,0 a 1,0
let transparentRed = UIColor(hexaString: "#FF0000", alpha: 0.5)  // r 1,0 g 0,0 b 0,0 a 0,5

另一种选择是将六值转换为无符号整数，并从中提取相应的值:

extension UIColor {
    convenience init(hexaString: String, alpha: CGFloat = 1) {
        self.init(hexa: UInt(hexaString.dropFirst(), radix: 16) ?? 0, alpha: alpha)
    }
    convenience init(hexa: UInt, alpha: CGFloat = 1) {
        self.init(red:   .init((hexa & 0xff0000) >> 16) / 255,
                  green: .init((hexa & 0xff00  ) >>  8) / 255,
                  blue:  .init( hexa & 0xff    )        / 255,
                  alpha: alpha)
    }
}

let purpleColor       = UIColor(hexaString: "#FF00FF")    // r 1,0 g 0,0 b 1,0 a 1,0
let transparentYellow = UIColor(hexaString: "#FFFF00", alpha: 0.5)  // r 1,0 g 1,0 b 0,0 a 0,5

除了颜色，我还喜欢保证alpha，所以我自己写类别

+ (UIColor *) colorWithHex:(int)color {

    float red = (color & 0xff000000) >> 24;
    float green = (color & 0x00ff0000) >> 16;
    float blue = (color & 0x0000ff00) >> 8;
    float alpha = (color & 0x000000ff);

    return [UIColor colorWithRed:red/255.0 green:green/255.0 blue:blue/255.0 alpha:alpha/255.0];
}

像这样很容易使用

[UIColor colorWithHex:0xFF0000FF]; //Red
[UIColor colorWithHex:0x00FF00FF]; //Green
[UIColor colorWithHex:0x00FF00FF]; //Blue
[UIColor colorWithHex:0x0000007F]; //transparent black

有cocoapod支持，这很好

https://github.com/mRs-/HexColors

// with hash
NSColor *colorWithHex = [NSColor colorWithHexString:@"#ff8942" alpha:1];

// wihtout hash
NSColor *secondColorWithHex = [NSColor colorWithHexString:@"ff8942" alpha:1];

// short handling
NSColor *shortColorWithHex = [NSColor colorWithHexString:@"fff" alpha:1]

Swift 2.0 - Xcode 7.2

为UIColor添加扩展。

文件-新建- Swift文件-命名。添加以下内容。

extension UIColor {
    convenience init(hexString:String) {
        let hexString:NSString = hexString.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
        let scanner            = NSScanner(string: hexString as String)
        if (hexString.hasPrefix("#")) {
            scanner.scanLocation = 1
        }

        var color:UInt32 = 0
        scanner.scanHexInt(&color)

        let mask = 0x000000FF
        let r = Int(color >> 16) & mask
        let g = Int(color >> 8) & mask
        let b = Int(color) & mask

        let red   = CGFloat(r) / 255.0
        let green = CGFloat(g) / 255.0
        let blue  = CGFloat(b) / 255.0
        self.init(red:red, green:green, blue:blue, alpha:1)
    }

    func toHexString() -> String {
        var r:CGFloat = 0
        var g:CGFloat = 0
        var b:CGFloat = 0
        var a:CGFloat = 0
        getRed(&r, green: &g, blue: &b, alpha: &a)
        let rgb:Int = (Int)(r*255)<<16 | (Int)(g*255)<<8 | (Int)(b*255)<<0
        return NSString(format:"#%06x", rgb) as String
    }        
}

用法:

Ex. Setting Button's color from hexCode.
    override func viewWillAppear(animated: Bool) {
        loginButton.tintColor = UIColor(hexString: " hex code here ")
}

Ex. Converting Button's current color to hex Code.

    override func viewWillAppear(animated: Bool) {
        let hexString = loginButton.tintColor.toHexString()
        print("HEX STRING: \(hexString)")

    }